FIG. 1 illustrates a network (Bluetooth piconet P1) 11 of radio transceiver units 1, 2, 3, 4, 5 and 7. The network is a radio frequency network suitable for transmitting voice information or data information between transceivers. The transmissions made are of low power, for example 0 to 20 dBm, and the transceiver units can effectively communicate over the range of a few tens or hundred of meters. The transceivers transmit and receive, in this example, in a microwave frequency band, illustratively 2.4 GHz. Interference in the piconet is reduced by changing the frequency at which each successive radio packet in the piconet is transmitted. A number of separate frequency channels are assigned each with a bandwidth of 1 MHz, and the frequency may hop at a rate of 1600 hops/s.
The transceiver 1 is the master M1 of the piconet P1 and the transceivers 2, 3, 4, 5 and 7 are slaves in the piconet P1. The transceiver 6 lies outside the range of transceiver 1 and is outside the piconet P1. There is only one master in a piconet. The master can directly communicate with each slave in its piconet but each slave can only directly communicate with the master. The piconet operates in a time division duplex fashion.
FIG. 2 illustrates a time frame 20 used by the master unit M1. The frame illustratively has slots 22 to 29 of equal length (625 microseconds). Each slot carries a packet of data and is allocated a different one of a sequence of hopping frequencies.
FIG. 3 illustrates a typical radio packet 30. The radio packet has a start 32 and contains three distinct portions: a first preamble portion contains an Access Code 34, a second portion contains a Header 36 and a third portion contains a Payload 38. The Access Code is a series of bits used in the network to identify the start of a radio packet. The Channel Access Code identifies a piconet and is included in all packets communicated in the piconet channel. The header 36 of a packet transmitted from the master to a slave contains the active member address (AM_ADDR) of the addressed slave which identifies the slave within the piconet. The payload 38 carries either transceiver control information or voice/data information.
In the Connection State, when the master and slaves are communicating, the packets sent in the piconet use the same channel access code (derived from Bluetooth device address BD_ADDR of the master unit) and the same frequency hopping sequence, the channel hopping sequence (derived from Bluetooth device address BD_ADDR of the master unit). The transceiver units are synchronised to a common time frame determined by the master unit and described in relation to FIG. 2. The frequency at which each radio packet is transmitted is determined by the phase of the channel hopping sequence. The phase varies with the master clock and the transmission frequency changes (hops) every 625 microseconds.
It would be desirable to be able to handover the slave transceiver 7 from the piconet P1 to another piconet P2 controlled by master M2 having overlapping radio coverage area with P1. FIG. 4 illustrates the scatternet formed after a handover to master M2. The piconet P2, referenced by numeral 12, comprises transceivers 1, 2, 6 and 7 with transceiver 2 the master M2.